Upscaling environment-friendly cavitation melt treatment (UltraMelt #2)

我们对金属的使用是如此重要，以至于它定义了人类文明的各个时期--从青铜器时代开始（公元前200年）。公元前3600年）至铁器时代（c。公元前1100年）。随着我们对金属和合金的掌握，现在越来越重视资源和环境。金属行业正在寻找新的方法，以可持续、经济和无污染的方式生产更轻、更强的材料。超声空化处理提供了一种途径，以满足这些目标。第二常见的结构金属铝的超声波处理通过抽空溶解的气体而引起脱气，从而导致孔隙率、晶粒细化以辅助成形性、固体或不混溶相的分散和分布以改善回收期间的机械性能等。尽管有这些好处，但将这种有前途的技术转移到工业上一直受到困难的困扰，特别是在处理大体积的液态金属的过程中，例如用于铸锭生产的“直接冷却”连续铸造。基础研究需要回答以下实际问题：什么是最佳熔体流动速率，最大限度地提高处理效率，同时最大限度地减少输入功率，成本和工厂的复杂性？加速治疗效果的最佳工作频率和声功率是多少？超声波功率源在熔体输送系统中相对于熔池几何形状的最佳位置是什么？这些问题的解决将为超声波熔体加工的广泛工业应用铺平道路，有利于改善轻质结构合金的性能，同时减轻目前使用污染性（Cl，F）的脱气或昂贵的（Zr，Ti，B，Ar）晶粒细化添加剂。充分利用建议者在非常成功的UltraMelt项目中获得的独特专业知识（22出版物），这项研究旨在通过开发一个综合的数值模型来应对有效处理大量液体的挑战，该模型耦合了所有涉及的物理：流体流动，传热，固化，声学和气泡动力学。格林威治将领导开发一种改进的空化模型，该模型基于波动方程和守恒定律，并应用于熔体中气泡破裂和运输的两相问题，及其与固体夹杂物的相互作用（例如，铝合金或任何金属间杂质的凝固前沿）。为了提高流动金属中超声空化处理的效率，将使用流槽导管。该过程相对于不同可调参数（源功率、频率、空化区时间、挡板位置.）的灵敏度将在流槽中熔体流动的3D模型中进行并行计算。该计算机模型将通过透明液体和铝的实验进行验证。水和透明有机合金实验将使用牛津布鲁克斯大学的PIV技术来测量气泡的大小，数量和位置，并将其与数值预测进行比较。将使用布鲁内尔大学的高速照相机和金刚石光源设施的X射线照相术，在真实的时间内观察金属间化合物碎裂和颗粒团分裂的机制。将与安东帕尔有限公司合作，使用独特的纳米压痕技术测量金属间杂质在熔融加工相关温度下的机械性能。将在布鲁内尔大学进行流槽管道中的空化压力测量，并将经验观察结果与模型预测进行比较。完全开发的模型将用于优化直接激冷铸造过程中熔体流动中的超声波熔体处理，并使用AMCC（Brunel，在Constellium的支持下）的中试规模设施和Kaiser Aluminum的工业规模设施进行验证。

Our use of metals is so important that it defines periods of human civilisation - from the Bronze Age (c. 3600 BC) to the Iron Age (c. 1100BC). With our present-day mastery of metals and alloys, the mounting emphasis is now on resources and the environment. The metals industry is looking at new ways to produce lighter, stronger materials in a sustainable, economical and pollution-free manner. Ultrasonic cavitation treatment offers a route to meet these goals. Ultrasonic treatment of the second commonest structural metal, aluminium, causes degassing through the evacuation of dissolved gases that lead to porosity, grain refinement to assist formability, dispersion and distribution of solid or immiscible phases to improve mechanical properties during recycling etc. In spite of the benefits, transfer of this promising technology to industry has been plagued by difficulties, especially in treating large volumes of liquid metal typical in processes such as 'Direct Chill' continuous casting for ingot production. Fundamental research is needed to answer the following practical questions: what is the optimum melt flow rate that maximises treatment efficiency whilst minimizing input power, cost, and plant complexity? What is the optimum operating frequency and acoustic power that accelerates the treatment effects? What is the optimum location of an ultrasonic power source in the melt transfer system in relation to the melt pool geometry? Answering these questions will pave the way for widespread industrial use of ultrasonic melt processing with the benefit of improving the properties of lightweight structural alloys, simultaneously alleviating the present use of polluting (Cl, F) for degassing or expensive (Zr, Ti, B, Ar) grain refinement additives.Capitalising on the unique expertise gained by the proposers during the highly successful UltraMelt project (22 publications), this research aims to answer the challenge of efficiently treating large liquid volumes by developing a comprehensive numerical model that couples all the physics involved: fluid flow, heat transfer, solidification, acoustics and bubble dynamics. Greenwich will lead the development of an improved cavitation model, based on the wave equation and conservation laws, and applied to the two-phase problem of bubble breakup and transport in the melt, and its interaction with solid inclusions (e.g. the solidification front of an aluminium alloy or of any intermetallic impurities present). To improve the efficiency of the ultrasonic cavitation treatment in flowing metal, a launder conduit will be used. The sensitivity of the process with respect to different adjustable parameters (source power, frequency, time in the cavitation zone, baffle location ...) will be examined with parallel computations in a 3D model of melt flow in the launder. This computer model will be validated by experiments in both transparent liquids and aluminium. Water and transparent organic alloy experiments will use a PIV technique by Oxford Brookes University to measure the size, number and positions of bubbles and compared these with the numerical predictions. Mechanisms of intermetallic fragmentation and particle cluster breakup will be observed in real time using a high speed camera at Brunel University and X-ray radiography at the Diamond Light Source facility. Mechanical properties of intermetallic impurities at temperatures relevant to melt processing will be measured using unique nano-indentation technique in collaboration with Anton Paar Ltd. Cavitation pressure measurements in launder conduits will be conducted at Brunel University and the empirical observations will be compared with model predictions. The fully-developed model will be used to optimise the ultrasonic melt treatment in melt flow during direct-chill casting and verified using pilot-scale facilities at AMCC (Brunel, with support of Constellium) and industrial-scale facilities at Kaiser Aluminum.